For a guy who takes stuff apart all the time, I can't believe you can't solve the A50/1.7 aperture ring problem. The leaf springs that push the A button out will fall off the lens and foul the aperture ring movement. I've repaired it on the A28/2.8. The repair is trivial, the dis-assembly isn't tough...just keep track of the little ball bearing that makes the clicks for the aperture stops.
Hee... not this one. The problem associated with the all plastic 'A' prime lenses (and some 'F' lenses too) has to do with the material being chosen, and the structural designs. I tried cleaning and relubricating but only worked for a week or so, then the problem came back. It was better if the bearing was removed, but not exactly a solution. 'A' lenses with metal body + plastic aperture ring are okay (like A50/1.4 or A70-210/4).
Alan Chan http://www.pbase.com/wlachan
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